The present invention relates to a measuring device which features sensors exhibiting a variation in impedance or in voltage, especially temperature sensors, which is suitable more particularly for a heating/air-conditioning installation.
In heating/air-conditioning installations, the temperature sensors for the air conditioning are generally passive components of thermistor type, and more particularly negative-temperature-coefficient thermistor (NTC) type.
They are generally biased by a calibration voltage source, for example at 5V, via a resistor, especially a precision resistor of 1% class.
The voltage measured at the terminals of the thermistor is next amplified and measured by a microprocessor-type thermal-regulation device.
Such a conventional device dictates, for each sensor, that two connecting wires be linked to the regulation card which the microprocessor includes.
In an air-conditioning system including 6 temperature sensors, 12 direct or indirect connections with the regulation card have to be made available, resulting in a high cost of the wiring harness and of the associated connections, and problems of reliability which result from the relative complexity of the assembly.
One object of the invention is to propose reducing the number of connection points of the sensors by at least two.
Another object of the invention is to reduce the number of analogue-measuring inputs of the regulation card.
Another object of the invention is to propose a device which is simpler and therefore of higher reliability.
At least one of the abovementioned objects is achieved by virtue of a measuring device intended especially for a heating/air-conditioning installation, and comprising sensors biased by at least one electrical power-supply source, characterised in that it includes at least one series branch featuring a first and a second terminal coupled to terminals of a said power-supply source, the said first branch featuring, on the one hand, a first and a second diode head to tail connected between the first and the second terminal of the series branch, and, on the other hand, a first and a second sensor connected in series between the first and the second terminal of the series branch, the common point between the first and the second diode being connected to the common point between the first and the second sensors, and in that it includes a changeover-switching device for reversing the direction of the said bias so that the first or the second sensor is traversed by a current.
The sensors may be of a type exhibiting a variation in impedance, temperature sensors in particular.
The device may be characterised in that at least one terminal of a said power-supply source is connected, on the one hand, to a bias resistor in series with a first voltage source having a first potential and, on the other hand, to a changeover-switching element, especially a transistor, exhibiting a first, non-conducting state and a second, conducting state, in order to take the said terminal to a second potential, the said bias resistor in series with the first voltage source and the changeover-switching element constituting a bistable device.
According to one advantageous embodiment, the device is characterised in that the first and the second terminal of the said series branch are each coupled to a said bistable device, and in that the said changeover-switching device is configured to place the changeover-switching element of one of the bistable devices in the first, conducting state and the changeover-switching element of the other bistable device in the second, non-conducting state alternately.
The device advantageously features n series branches BS1 . . . BSn connected in series and coupled to nxe2x88x921 power-supply terminals BA1 . . . BAnxe2x88x921.
According to one preferred embodiment, the device features at least one series branch coupled to a power-supply terminal of rank P, BSp, and to a power-supply terminal of rank (p+q), BSp+q, with q greater than 1.
The device may be characterised in that it features a microprocessor for switching over at least one changeover-switching device and for measuring at least one voltage developed by a sensor, especially a temperature sensor. The said changeover switching is preferably sequential in such a way as to allow reading of each of the sensors.
Finally, the invention relates to a heating and/or air-conditioning installation as defined above.